CEN/SS N21 - Gaseous fuels and combustible gas

This document describes the precision that can be expected from the gas chromatographic method that is set up in accordance with ISO 6974-1. The stated precision provides values for the magnitude of variability that can be expected between test results when the method described in ISO 6974-1 is applied in one or more competent laboratories. This document also gives guidance on the assessment of bias.

ISO 6974-5:2014 describes a gas chromatographic method for the quantitative determination of the content of nitrogen, carbon dioxide and C1 to C5 hydrocarbons individually and a composite C6+ measurement, which represents all hydrocarbons of carbon number 6 and above in natural gas samples.

2011-04-08 EMA: Draft for // final vote received in ISO/CS (see notification of 2011-04-06 in dataservice).

This part of ISO 6974 describes the process required to determine the uncertainty associated with the mole
fraction for each component from a natural gas analysis in accordance with ISO 6974‑1.

ISO 19739:2004 specifies the determination of hydrogen sulfide, carbonyl sulfide, C1 to C4 thiols, sulfides and tetrahydrothiophene (THT) using gas chromatography (GC). Depending on the method chosen from those given in its annexes, the application ranges for the determination of sulfur compounds can vary, but whichever of the methods is used, its requirements apply.

ISO 6974-6:2002 describes a gas chromatographic method for the quantitative determination of the content of helium, hydrogen, oxygen, nitrogen, carbon dioxide and C1 to C8 hydrocarbons in natural gas samples using three capillary columns. This method is applicable to the determination of these gases within the mole fraction ranges varying from 0,000 1 % to 40 %, depending on the component analysed, and is commonly used for laboratory applications. However, it is only applicable to methane within the mole fraction range of 40 % to 100 %. These ranges do not represent the limits of detection, but the limits within which the stated precision of the method applies. Although one or more components in a sample may not be present at detectable levels, the method can still be applicable.
ISO 6974-6:2002 is only applicable if used in conjunction with ISO 6974-1:2000 and ISO 6974-2:2001.
This method can also be applicable to the analysis of natural gas substitutes. Additional information on the applicability of this method to the determination of natural gas substitutes is also given where relevant.

This International Standard describes the principles of, and general requirements for, two gravimetric methods for
the determination of the potential hydrocarbon liquid content of natural gas, or similar gas, at a given pressure and
temperature. Two methods are specified in this International Standard to determine the amount of condensate in a
sample gas:
_ Method A: a manual weighing method;
_ Method B: an indirect automatic weighing method based on the indication of the pressure difference caused by
the accumulation of condensate in a vertical tube.
The manual weighing method is a reference method for the indirect automatic method (Method B). The indirect
automatic method (Method B) is suitable for semi-continuous control.
NOTE Unless otherwise specified, gas volumes are in cubic metres at 273,15 K and 101,325 kPa.

Describes a method of determining the water content of natural gas under pressure of more than 1 MPa. Also applicable to natural gas, containing hydrogen sulfide with a water concentration of 10 mg/m^3 or more.

Migrated from Progress Sheet (TC Comment) (2000-07-10): WIs 020-025 = result of the splitting of WI 011 (CC/991102 at the request of ++ R. R{migy and A. Pirlet)

Migrated from Progress Sheet (TC Comment) (2000-07-10): See mail from P. Pieters dated on 98-03-31 (BL)

The principle of the method specified is passing a measured volume of gas through the titration cell, where the water is absorbed by the anodic solution. The iodine required for the determination of water by the Karl Fischer reaction is generated coulometrically from iodide. The quantity of electricity is directly proportional to the mass of iodine generated and hence to the mass of water determined. Applies to natural gas and other gases which do not react with Karl Fischer reagents. Is applicable to water concentrations between 5 mg/cm^3 and 5000 mg/cm^3.

The principle of the method specified is passing a measured volume of gas through a cell containing a relatively small volume of absorbent solution. Water in the gas is extracted by the absorbent solution and subsequently titrated with Karl Fischer reagent. The design of the cell and the absorbent solution are chosen so as to ensure efficient collection of the water at the high flowrates necessary. Is applicable to water concentrations between 5 mg/cm^3 and 5000 mg/cm^3.

Specifies general requirements for the determination. The principle of the method is reaction of water present in the test sample with iodine and sulfur-dioxide in a pyridine/methanol mixture (Karl Fischer reagent). ISO 10101-2 and ISO 10101-3 specify two individual methods of determination.

ISO 6326-1:2007 gives a brief description of standardized methods that can be used for the determination of sulfur compounds in natural gas.
The principle of each method is described generally, the range of concentrations for which the method is suitable is indicated, and the analytical range and precision of each method is given. It should enable the user to select judiciously the proper method for the application being considered. Sulfur analysis is performed in order to determine total sulfur, sulfur contained in specific groups [e.g. thiols (mercaptans)], individual sulfur compounds and specific groups of sulfur compounds.
The available standardized methods in the field of sulfur analysis are the Wickbold combustion method for total sulfur determination (ISO 4260); the Lingener combustion method for total sulfur determination (ISO 6326-5); gas chromatography for determination of individual sulfur compounds (ISO 19739); potentiometry for determination of hydrogen sulfide, carbonyl sulfide and thiol compounds (ISO 6326-3).

Specifies a method for the determination of total sulphur in natural gas. It is applicable to gases with sulphur contents between 0,5 mg/m3 and 1 000 mg/m3. With a total sulphur content of more than 0,1 mg sulphur in the absorption solution, visual titration with an indicator can be chosen, whereas for lower contents turbidimetric titration is preferable.

Specifies a potentiometric method for components in natural gas in the concentration range equal to or above 1 mg/m3. The gas must be free of dust, mist, oxygen, hydrogen cyanide and carbon disulfide. The method is not recommended for gases containing more than approximately 1,5 % (V/V) carbon dioxide.

ISO 6145-1:2003 specifies the calibration methods involved in the preparation of gas mixtures by dynamic volumetric techniques. It also gives a brief presentation of a non-exhaustive list of examples of dynamic volumetric techniques which are described in more detail in other parts of ISO 6145.

ISO 6145-7:2009 specifies a method for continuous production of calibration gas mixtures, containing two or more components, from pure gases or other gas mixtures by use of commercially available thermal mass-flow controllers.
If this method is employed for the preparation of calibration gas mixtures, the optimum performance is as follows: the relative expanded uncertainty of measurement, U, obtained by multiplying the combined standard uncertainty by a coverage factor k = 2, is not greater than 2 %.
If pre-mixed gases are used instead of pure gases, mole fractions below 10-6 can be obtained. The measurement of mass flow is not absolute and the flow controller requires independent calibration.
The merits of the method are that a large quantity of the gas mixture can be prepared on a continuous basis and that multicomponent mixtures can be prepared as readily as binary mixtures if the appropriate number of thermal mass-flow controllers is utilized.

Migrated from Progress Sheet (TC Comment) (2000-07-10): WIs 020-025 = result of the splitting of WI 011 (CC/991102 at the request of ++ R. R{migy and A. Pirlet)

ISO 6145-6:2003 specifies a method for the continuous production of calibration gas mixtures, containing two or more components, from pure gases or other gas mixtures by use of critical orifice systems. By selection of appropriate combinations of orifices and with the use of pure gases, the volume fraction of the calibration component in the calibration gas mixture can be varied by a factor of 104. Additionally, it can be changed by a factor of 102 by changing the initial pressures in the orifice systems. The uncertainty of the method depends mainly upon the flow calibration method and the variations in temperature and outlet pressure. The relative expanded uncertainty in the volume fraction obtainable for a binary mixture (at a coverage factor of 2) is 3 %.
If pre-mixed gases are used instead of pure gases, much lower volume fractions can be obtained. The mass flow rates or volume flow rates, from which the mass or volume fractions are determined, can be calculated and can be independently measured by a suitable method given in ISO 6145-1.
The merits of the method are that multi-component mixtures can be prepared as readily as binary mixtures if the appropriate number of orifices is utilized, and that a large quantity of calibration gas mixture can be prepared on a continuous basis. The range of flow rates can be from several millilitres per minute to approximately 10 l/min.
Although particularly applicable to preparation of gas mixtures at barometric pressure, the method also provides a means of preparation of calibration gas mixtures at pressures above barometric pressure.

ISO 16664:2004 describes factors that may influence the composition of pure gases and homogeneous gas mixtures used for calibration purposes. ISO 16664:2004 only applies to gases or gas mixtures that are within the "utilization period", and it pays special attention to
storage of calibration gas cylinders;
calibration gas withdrawal from cylinders;
transfer of calibration gas from cylinders to the point of calibration.
ISO 16664:2004 also outlines a method of assessing the stability for a gas mixture, and takes into account the gas composition uncertainty given on the certificate and the users measurement uncertainty.

Specifies the gravimetric method for the preparation of reference gas mixtures in cylinders and is intended for the preparation of calibration gas mixtures whose target accuracy is defined a priori. It is applicable only to mixtures of gaseous, or totally vaporized components which do not react with each other or with the cylinder walls. A procedure is given for the preparation strategy that is based upon preset uncertainty levels of the composition of the final mixture. Multi-component gas mixtures and multiple dilution mixtures are included in this standard and are considered to be special cases of single component weighings.

Specifies requirements for certificates for pure gases and for homogeneous gas mixtures to be used as calibration gases. Specifies the minimum information (mandatory data) required and additional information (optional data) recommended for characterizing a pure gas, or a homogeneous gas mixture, supplied under pressure in a cylinder or other container.

Migrated from Progress Sheet (TC Comment) (2000-07-10): WIs 020-025 = result of the splitting of WI 011 (CC/991102 at the request of ++ R. R{migy and A. Pirlet)

Describes a method of assessing whether an analytical system for natural gas is satisfactory provided that the analytical requirements have been clearly defined and the analytical and calibration procedures have been fully described.

Migrated from Progress Sheet (TC Comment) (2000-07-10): WIs 020-025 = result of the splitting of WI 011 (CC/991102 at the request of ++ R. R{migy and A. Pirlet)

Migrated from Progress Sheet (TC Comment) (2000-07-10): WIs 020-025 = result of the splitting of WI 011 (CC/991102 at the request of ++ R. R{migy and A. Pirlet)

2009-12-02 ANP: Due to an error in the CEN database, the above listed standard had not been given the status of "Withdrawn" after publication of the superseding standard.

CMC - Including Technical Corrigendum 1 added in title and foreword